The present invention relates to a method for regulating the heat radiated by the glazings of vehicle interiors, as well as self-shading, thermally comfortable glass in vehicles.
It is a known fact in climate control technology that the thermal comfort of people in enclosed spaces depends on an even thermal balance between the person and his surroundings. Substantial thermal comfort or a comfortable feeling of warmth is achieved when the heat produced by the person is equal to the heat emitted to his surroundings. Important external factors influencing thermal comfort are the properties of ambient air, in particular temperature, humidity and velocity, as well as radiation, in particular the heat radiated by the surrounding surfaces.
The interplay between the properties of ambient air and radiation from the surrounding surfaces can, to a certain extent, result in an even thermal balance. Thus, low air temperatures can be partially equalized through increased thermal radiation or radiation temperature. Conversely, high radiation temperatures must be equalized by supplying cold air.
In enclosed vehicles, the interplay between air temperature, air flow, and radiant heat has a particular effect on the thermal comfort perceived by the passengers.
In the case of low outside temperatures, also referred to below as the winter situation, the temperatures of the surrounding surfaces are relatively low. This applies in particular to vehicle glazings that, unlike the double glazings common in building technology, are constructed of only a single glazing, or single pane, with poor thermal insulation properties. As a result, the inside of the glass has a low radiation temperature and correspondingly low thermal radiation. Passengers find the proximity of these “cold-radiating” surfaces to be uncomfortable. This is particularly true of roof glazings, where the head area is in close proximity to the cold surface.
In the “summer situation S,” not only does a high outside temperature prevail, but also, in particular, a high level of incident sunlight. The heat radiated into the vehicle forms the lion's share of the heat added to the thermal balance inside the vehicle. To reduce incident sunlight, the glass is typically shaded on the inside. For reasons of comfort, self-shading glazing is also used nowadays. It functions completely without the need for mechanical shading devices such as blinds or sliding panels.
Self-shading glazings operate by reducing transparency by increasing light absorption, thereby darkening the vehicle interior. They are used as protection against glare and heat. Self-darkening glass or laminated glass is used for self-shading glazings, usually electrochrome glass or glass with SPD (suspended particle device) films. In both cases, the transmission of light is switched from bright transmission to dark transmission through an external electrical pulse. As used herein, “bright transmission” of a glazing refers to the percentage of incident light transmitted through the glazing in an undarkened state, and “dark transmission” of a glazing refers to the percentage of incident light transmitted through the glazing in a darkened state. The structure and function of SPD films according to the definition of the species are known, for example, from European Patent Document EP 0 551 138 B1. The structure and function of electrochrome glass or laminate glass according to the definition of the species are known, for example, from European Patent Document EP 0 408 427 A1 and European Patent Document EP0 470 597A2.
The radiation absorbed by the darkened glass is largely converted to heat. When the glazing is shaded in the presence of incident sunlight (the summer situation), this substantially raises the temperature. It is known that radiant power Q of a body is proportionate to four times its surface temperature To. This is why shading the glazing in the presence of incident sunlight, also referred to below as the summer situation, substantially increases thermal radiation. Thermal radiation occurs mainly in the infrared (IR) range, thermal IR having a maximum wavelength ranging from 8 μm to 12 μm and thus accounting for the main component. Near-IR, having wavelengths from approximately 0.1 μm to 2 μm, contributes much less to thermal radiation. The radiation of the hot surface inside the vehicle helps increase the temperature to an undesirable extent and is felt to be extremely unpleasant.
A system that makes it possible to increase thermal comfort in passenger aircraft in the case of low outside temperatures or cold surrounding surfaces is known from German Unexamined Patent Application DE-OS 100 27 925. This is accomplished by applying to the inner wall of the cabin a low-emission or LE layer that is suitable for reflecting the infrared radiation, or the thermal radiation, back into the interior. The LE layer is preferably made of a doped and conductive tin oxide (SnO) material. This system does not take into account the summer situation.